Figure 2.1 Manifold/vacuum system used to introduce gases into the 3 L reaction flask. Valves controlling gas flow are labeled as V1 – V8, while stopcocks controlling gas flow are labeled as S1 and S2. It is worth noting that while Valves 1, 2, and 6, and Stopcock 1 are referred to explicitly in the protocol, the other valves and stopcock in the manifold shown here are useful for adding or removing volume (i.e. holding flasks) to or from the manifold. For example, when introducing gases into the manifold at relatively high pressures (approximately 500 mmHg or greater), it is advised that the experimenter makes use of all purge flasks attached to the manifold to increase the accessible volume of the manifold and help minimize the risk of over-pressuring the manifold.1. Setting Up a Manifold/Vacuum SystemUse a glass manifold to introduce gases into the reaction flask. This manifold can be purchased or constructed by a glass-blowing facility, but must include vacuum-tight ports that can be connected to a vacuum system, gas cylinders, a vacuum gauge, and the reaction vessel.Use ground glass joints and glass plugs with valves on the manifold. Ensure that all O-rings on the plugs are capable of making the necessary seals. If using glass joints, a sufficient amount of vacuum grease can be applied to help make a seal, if necessary. Silicone vacuum grease can be used to avoid potential organic contamination.Use glass stopcocks on the manifold. Apply the minimum amount of vacuum grease necessary to make a seal.Measure the manifold volume. This volume will be used for calculations related to final gas pressures in the 3 L reaction flask and should be known as precisely as possible.Unless the manifold has enough connections to accommodate all gas cylinders simultaneously, connect one cylinder at a time to the manifold. Include in this connection, a tap allowing the manifold to be isolated from the ambient atmosphere.Use suitable, clean, inert, and chemical and leak resistant tubing and ultratorr vacuum fittings to connect the gas cylinders to the manifold. Ultratorr fittings, are to be finger-tightened.Connect to the manifold, a vacuum pump capable of establishing a vacuum of <1 mmHg. The vacuum pump exhaust should be located within the fume hood, or properly vented by other means.To ensure rapid attainment of vacuum and to protect the pump, insert a trap between the manifold and the vacuum pump. A liquid nitrogen finger-trap is recommended as it will prevent volatiles such as NH3, CO2, and H2O from entering the pump. Care should be taken, as trapped volatiles, upon warming, may overpressure the manifold and result in glass rupture.Connect to the manifold, a manometer or other vacuum gauge capable of 1 mmHg resolution or better. While various devices can be used, a mercury manometer is preferable as mercury is fairly nonreactive.Measure and record the ambient temperature using a suitable thermometer.2. Preparation of Reaction FlaskHeat all glassware at 500 °C for at least 3 hr in air prior to use, to remove organic contaminants.Clean the tungsten electrodes by gently washing with clean laboratory wipes and methanol, and drying in air.Pour 200 ml of ultrapure water (18.2 M? cm, <5 ppb TOC) into the 3 L reaction flask.Introduce a cleaned and sterilized magnetic stir bar, which will ensure rapid dissolution of soluble gases and mixing of reactants during the experiment.Attach the tungsten electrodes to the 3 L reaction flask using a minimal amount of vacuum grease, with tips separated by approximately 1 cm inside the flask. Fasten with clips.Insert an adapter with a built-in stopcock into the neck of the 3 L reaction flask and secure with a clip.Attach the 3 L reaction flask to the gas manifold via the adapter. Use a clip or clamp to help secure the flask.Lightly grease all connections to ensure a good vacuum seal.Open all valves and stopcocks on the manifold, except Valve 6 and Stopcock 1 (Figure 2.1), and turn on the vacuum pump to evacuate the manifold. Once a stable vacuum reading of <1 mmHg has been attained, close Valve 1 and allow the manifold to sit for ~15 min to check for vacuum leaks. If none are detected, proceed to step 2.8. Otherwise troubleshoot the various connections until the leaks can be identified and fixed.Apply magnetic stirring to the reaction vessel. Open Valve 1 and Stopcock 1 (Figure 2.1) to evacuate the headspace of the 3 L reaction flask until the pressure has reached <1 mmHg.Close Valve 1 (Figure 2.1) and monitor the pressure inside the 3 L reaction flask. The measured pressure should increase to the vapor pressure of water. To ensure that no leaks exist, wait ~5 min at this stage. If the pressure (as read on the manometer) increases while Valve 1 is closed during this step, check for leaks in Stopcock 1 and the various reaction flask connections. If no leak is found, proceed to the next step.3. Introduction of Gaseous NH3Calculate the necessary pressure of gaseous NH3 to introduce into the manifold such that 200 mmHg of NH3 will be introduced into the reaction flask. Details on how to do this are provided in the calculation section included in the protocol.Close Valves 1 and 6, and Stopcock 1 (Figure 2.1) before introducing any gas into the manifold. Leave the other valves and stopcock open.Introduce NH3 into the manifold until a small pressure (approximately 10 mmHg) is reached and then evacuate the manifold to a pressure of <1 mmHg by opening Valve 1 (Figure 2.1). Repeat 3 times.Introduce NH3 into the manifold to reach the pressure determined in step 3.1.Open Stopcock 1 (Figure 2.1) to introduce 200 mmHg of NH3 into the 3 L reaction flask. The NH3 will dissolve in the water in the reaction flask and the pressure will fall slowly.Once the pressure stops dropping, close Stopcock 1 (Figure 2.1) and record the pressure read by the manometer. This value represents the pressure inside the flask and will be used to calculate the pressures for other gases that will be introduced into the manifold later.Open Valve 1 (Figure 2.1) to evacuate the manifold to a pressure of <1 mmHg.Close Valve 2 (Figure 2.1) and disconnect the NH3 gas cylinder from the manifold.4. Introduction of CH4Calculate the necessary pressure of CH4 to be introduced into the manifold such that 200 mmHg of CH4 will be introduced into the 3 L reaction flask. Example calculations are shown in the calculation section included in the protocol.Connect the CH4 gas cylinder to the manifold.Open all valves and stopcocks, except Valve 6 and Stopcock 1 (Figure 2.1), and evacuate the manifold to a pressure of <1 mmHg.Close Valve 1 once the manifold has been evacuated (Figure 2.1).Introduce CH4 into the manifold until a small pressure (approximately 10 mmHg) is obtained. This purges the line of any contaminant gases from preceding steps. Open Valve 1 (Figure 2.1) to evacuate the manifold to <1 mmHg. Repeat 2x more.Introduce CH4 into the manifold until the pressure calculated in step 4.1, is reached.Open Stopcock 1 (Figure 2.1) to introduce 200 mmHg of CH4 into the 3 L reaction flask.Close Stopcock 1 once the intended pressure of CH4 has been introduced into the 3 L reaction flask (Figure 2.1) and record the pressure measured by the manometer.Open Valve 1 (Figure 2.1) to evacuate the manifold to <1 mmHg.Close Valve 2 (Figure 2.1) and disconnect the CH4 cylinder from the manifold.5. Introduction of Further Gases (e.g. N2)At this point, it is not necessary to introduce additional gases. However, if desired, it is recommended to add 100 mmHg of N2. In this case, calculate the necessary pressure of N2 to be introduced into the manifold such that 100 mmHg of N2 will be introduced into the 3 L reaction flask. Example calculations are shown in the calculation section included in the protocol.Connect the N2 gas cylinder to the manifold.Open all valves and stopcocks, except Valve 6 and Stopcock 1 (Figure 2.1), and evacuate the manifold to a pressure of <1 mmHg.Close Valve 1 once the manifold has been evacuated (Figure 2.1).Introduce N2 into the manifold until a small pressure (approximately 10 mmHg) is obtained. Open Valve 1 (Figure 2.1) to evacuate the manifold to <1 mmHg. Repeat 2 more times.Introduce N2 into the manifold until the pressure calculated in step 5.1 is reached.Open Stopcock 1 (Figure 2.1) to introduce 100 mmHg of N2 into the reaction flask.Close Stopcock 1 once the intended pressure of N2 has been introduced into the reaction flask, (Figure 2.1) and record the pressure using the manometer.Open Valve 1 (Figure 2.1) to evacuate the manifold to <1 mmHg.Close Valve 2 (Figure 2.1) and disconnect the N2 cylinder from the manifold.6. Beginning the ExperimentDetach the reaction flask from the manifold by closing Stopcock 1 and Valve 1 (Figure 2.1) once all gases have been introduced into the reaction flask, so that ambient air may enter the manifold and bring the manifold up to ambient pressure.After carefully disconnecting the reaction flask from the manifold, set the flask somewhere it will not be disturbed (e.g. inside an empty fume hood).Disconnect the vacuum pump and carefully remove the cold trap and allow venting inside a fully operational fume hood.Secure the Tesla coil connected to the high frequency spark generator.Connect the opposite tungsten electrode to an electrical ground to enable the efficient passage of electrical current across the gap between the two electrodes.Set the output voltage of the spark generator to approximately 30,000 V, as detailed by documents available from the manufacturer.Prior to initiating the spark, close the fume hood sash, to serve as a safety shield between the apparatus and the experimenter. Turn the Tesla coil on to start the experiment, and allow sparking to continue for 2 weeks (or other desired period) in 1 hr on/off cycles.